An example of a sighting instrument of the type to which the present invention relates is described in U.S. Pat. No. 4,859,058, the disclosure of which is incorporated herein by reference thereto.
Such a device comprises an electronic light dot reticle sight of relatively simple, lightweight construction that enables rapid and precise aiming of a firearm, even under low light conditions. A conventional implementation is of a double-barreled side-by-side construction, with a tubular battery or circuitry housing supported by a brace or strut in spaced position adjacent a firearm mountable tubular lens housing.
The lens housing has front and rear apertures and contains a lens system having a rearwardly facing concave light reflecting surface that serves as a semi-transparent mirror to produce an image of a small electric light source. The semi-transparent mirror surface and the light source are arranged so that a dot point image will be perceived ahead of the mirror surface by an observer looking through the sight, to act as a sighting mark between the observer's eye and the target. The lens system is mounted in a tube resiliently supported for variation in orientation by means of vertical and horizontal positioning screws that contact the tube to provide elevation and cross-angle or windage adjustment control for the sight by positioning the dot point image relative to the lens housing axis. The adjustment screws are marked in minute-of-angle increments, are coin turnable, and are shielded by protective dust covers.
In the conventional configuration shown in U.S. Pat. No. 4,859,058, the battery or circuitry housing has a removable cover at one end for replacement of two mercury cells that power the light source located in the lens housing. An on/off switch and intensity control for the light (and thus the dot image sighting mark) are provided at the other end of the battery housing in the form of a rotation knob rheostat. The lens housing is provided with strap brackets for mounting on a firearm, and the battery housing is joined in spaced position alongside the lens housing by a radially-directed supporting brace or strut. Electrical connection between the rheostat and power source in the battery housing and the light in the lens housing is established by wires running through the brace.
In the typical conventional configuration, the battery housing is located to the left or right of and slightly below the lens housing, so that its rheostat post and power cells are coaxially aligned in general parallel relationship to the optical axis, and thus the gun axis. The cells are loaded in the housing and acted upon by a spring which provides a stabilizing bias in the presences of firing forces to maintain the position of the cells.
Guns such as air guns have a "forward" recoil, due to the spring hitting the bottom of the air cylinder. Other guns have a backward recoil due to the firing of the projectile.